[llvm-readobj] Improve printing of Windows ARM packed unwind info

Fix a couple minor details in the existing logic for calculating
saved registers and stack adjustment.

Synthesize the corresponding prologues and epilogues and print them.
(This supersedes the previous printout of one single list of stored
registers; as there's lots of minor nuance differences in how
registers are pushed/popped in various corner cases, it's better to
print the full prologue/epilogue instead of trying to condense it
into one single list.)

Print the raw values of the fields Reg, R, L (LinkRegister) and C
(Chaining) instead of only printing the derived values.

Differential Revision: https://reviews.llvm.org/D125644